Purpose In vitro and in vivo studies suggest adding a second agent to ceftazidime/avibactam (CZA) to enhance bactericidal activity against Pseudomonas aeruginosa (PA). Nevertheless, evidence supporting this practice is scarce. Methods We conducted a retrospective cohort study of patients admitted to 9 Italian hospitals with microbiologically confirmed PA infection and treated with CZA alone or in combination from 01/01/2015 to...